Hi,
It is the same as with real PLC. In following link You can see what You have to do. Then start PLCSIM (change connection to PLCSIM(PROFIBUS)), start runtime in WinCC Flex, and You can to simulate.
Link Sample.zip http://plcforum.uz.ua//Sample.zip
Size: 2714 KB
My version or Step7 is 5.4 + SP4 and WinCC Flex is 2008 SP1 + HF2
regards